JONESBORO  A gunman who shot and killed three people and injured four more in northeast Arkansas was an acquaintance or friend of the victims, police said Sunday, but noted the motive still is unknown.

Jonesboro Police Sgt. Doug Formon identified the shooter as Porfirio Hernandez, 40, who recently had been released from a mental health treatment facility. Formon did not give further details in an email to The Associated Press.

Formon said police responded to the first shooting about 1 p.m. Saturday. Chrisanto Islas, 38, and Floza Davila, 12, were killed there and four others were injured. Survivors and witnesses at the house identified Hernandez as the sole gunman and provided a description of him and the vehicle he was driving.

About 20 minutes later, police responded to a second report of a shooting about three miles away, where they found Richardo Lopez, 31, dead. A witness described a vehicle matching the description from the Jonesboro home.

Investigators then received a report that a car matching the description of the shooter's had been located on a rural county road. Deputies discovered Hernandez dead with an apparent self-inflicted gunshot wound to the head.

Police said the three people are in critical condition in hospitals in Memphis, Tennessee: Augusten Hernandez, 43; Ayde Davila, 36; and Anquel Islas, 8. A 10-year-old boy, Brayam Davila, is in stable condition.

It wasn't immediately clear how Porfirio Hernandez and the seven victims knew one another.